In semiconductor fabrication, integrated circuit (IC) devices are becoming smaller, faster, and more efficient, leading toward higher densities of IC devices on chips. As this trend continues, reducing critical dimension (CD) is often important. The critical dimension is the dimension of the smallest feature (e.g., interconnect line, contact, trench) that can be formed during semiconductor device fabrication. Lowering critical dimensions facilitates formation of smaller components and, therefore, increased device density. Accordingly, achieving a desired critical dimension is often a goal of patterning processes.
FIGS. 1 and 2 illustrate a stage in a conventional patterning process. According to the process, photolithography techniques are used to define a pattern in a patterning material 112 formed above a base material 114, which may be supported by a substrate 116, to be patterned. In some instances, the substrate 116 may have patterning material 112 located directly thereon for patterning of the substrate 116. The patterning material 112 is selectively exposed to an energy source, such as an actinic energy, to alter the material characteristics of the patterning material 112 in select regions such that the altered regions will be more or less susceptible to development by a developer. Such susceptibility and the response of the patterning material 112 to exposure depend upon the patterning material chemistry. For example, if the patterning material 112 is formulated as a positive tone photoresist material, exposed regions become more susceptible to development while unexposed regions (e.g., masked regions) remain less susceptible. However, if the patterning material 112 is formulated as a negative tone photoresist material, exposed regions become less susceptible to development, and the unexposed regions (e.g., masked regions) remain susceptible. Post exposure, the development-susceptible regions are selectively removed to define a pattern, referred to herein as an “initial pattern” 118, of initial features 120, which may be elongate features. As illustrated in FIGS. 1 and 2, the initial features 120 of the initial pattern 118 may be separated from one another by trenches 122, each of which may expose an upper surface 124 of the base material 114. Each initial feature 120 may be formed so as to define an initial width Wi and an initial height Hi. The initial width Wi may be of the smallest dimension achievable due to limitations of the photolithography process employed. Nonetheless, the initial width Wi may not be small enough to accommodate patterning of the base material 114 at a desired critical dimension. For example, the initial width Wi may be on the order of about 40 nm to about 50 nm, while the desired critical dimension may be on the order of about 20 nm to about 30 nm. Accordingly, the initial pattern 118 of the plurality of initial features 120 may be subjected to a trimming process to reduce the width of the initial features 120.
During a conventional trimming process, the initial features 120 may be exposed to an etchant, referred to herein as a “trimming chemistry.” The trimming chemistry may be used to remove material laterally and vertically from the initial features 120 at sidewalls 126 and a top surface 128, respectively, to form, as illustrated in FIGS. 3 and 4, a trimmed pattern 130 of trimmed features 132 (also referred to herein as a “pattern of trimmed features”). In embodiments in which the initial features 120 are elongate features, the trimmed features 132 may also be elongate features, but with a narrower width (i.e., a smaller lateral dimension). The trimmed features 132 may be spaced from one another by enlarged trenches 134 exposing more of the upper surface 124 of the base material 114 than was exposed by the trenches 122 prior to the trimming process.
Each of the trimmed features 132 defines a trimmed width Wt and a trimmed height Ht. Theoretically, the trimmed width Wt may correspond to a desired critical dimension, and each of the trimmed features 132 includes trimmed sidewalls 136 that define a smooth, vertical, elevational profile terminating at a 90° angle with a planarized, trimmed top surface 138. In actual practice, however, conventional trimming chemistries and processes often lead to formation of trimmed features 132 having rough (non-uniform) trimmed sidewalls 136 that are not straight and vertical and that do not meet a planarized top surface 138 at a 90° angle. As illustrated in FIG. 5, the trimmed sidewalls 136 may include peaks and valleys that contribute to a nonuniform feature width roughness (e.g., line width roughness (LWR)) and nonuniform space width roughness (SWR). Thus, at various points along a length of a trimmed feature 132, the trimmed width Wt may vary; hence, as illustrated in FIG. 5, trimmed widths Wt1, Wt2, Wt3, and Wt4 are not uniform. Likewise, at various points along a length of the enlarged trenches 134, a trench width (e.g., Tt1, Tt2, Tt3, and Tt4) varies.
As illustrated in FIGS. 6A through 6J, conventional trimming chemistries and processes may also lead to formation of trimmed features 132A-132E and trimmed patterns 130E-130J having undesirable cross-sectional profiles that exhibit one or more defects. Conventional trimming chemistries include, for example, sulfur dioxide alone (i.e., SO2, which may produce trimmed pattern 130F of FIG. 6F), sulfur dioxide and oxygen (i.e., SO2 and O2, which may produce trimmed pattern 130G of FIG. 6G), oxygen and a halogen-based compound without sulfur dioxide (e.g., Cl2 and O2, which may produce trimmed pattern 130H of FIG. 6H), oxygen with a halogen-based compound and an organohalogen compound, but without sulfur dioxide (e.g., Cl2, O2, CF4, and CH2O2, which may produce trimmed pattern 130I of FIG. 6I), or oxygen with an organohalogen compound and without sulfur dioxide (e.g., CF4 and O2, which may produce trimmed pattern 130J of FIG. 6J). As such, conventional trimming chemistries may produce trimmed features having slanted profiles (e.g., trimmed features 132A, 132E and trimmed patterns 130F, 130J), sloped sidewalls (e.g., trimmed features 132A, 132B and trimmed pattern 130I), top coating material 140 overhang regions 142 (e.g., trimmed feature 132C), line collapse or wobbling (e.g., trimmed feature 132D and trimmed pattern 130J), top tapering (e.g., trimmed features 132A, 132E and trimmed patterns 130E-130I), bottom tapering (e.g., trimmed feature 132B and trimmed pattern 130I), and excessive height loss (e.g., trimmed feature 132E and trimmed patterns 130F, 130G). Each of the imperfections with regard to feature width roughness, space width roughness, trimmed feature profile, and feature height may lead to formation of errors in structures formed in the base material 114 when the trimmed pattern 130 is transferred to the base material 114. It is contemplated that avoiding such imperfections may present even more of a challenge as critical dimensions decrease.